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Title on the Effect of Wind on Wave Overtopping on Vertical Seawalls Author(S) View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Kyoto University Research Information Repository On the Effect of Wind on Wave Overtopping on Vertical Title Seawalls Author(s) IWAGAKI, Yuichi; TSUCHIYA, Yoshito; INOUE, Masao Bulletin of the Disaster Prevention Research Institute (1966), Citation 16(1): 11-30 Issue Date 1966-09 URL http://hdl.handle.net/2433/124717 Right Type Departmental Bulletin Paper Textversion publisher Kyoto University Bull. Disas. Prey. Res. Inst. Kyoto Univ., Vol. 16, Part 1, No. 105, Sept., 1965 On the Effect of Wind on Wave Overtopping on Vertical Seawalls By Yuichi IWAGAKI, Yoshito TSUCHIYA and Masao INOUE (Manuscript received June 30. 1966) Synopsis In designing seawalls and seadikes, it is very important to estimate the quantity of wave overtopping on them as exactly as possible. The estimation, however, is difficult because of complicated phenomenaof wave overtopping, and in particular the effect of wind on wave overtopping is entirely unknown. With this in view, the authors have begun the study to disclose the effect of wind on wave overtopping quantitatively. As a first step of the study. the present paper describes some experimental results of wave overtoppingon vertical seawalls for the wave steepnesses of 0.01 and 0.02, accompanied with wind created by a high-speed wind-wave tunnel, which is 0.8 m wide. 2.3m to 4.0 m high and 40 m long, having a blower of 100HP and a wave generator of submerged piston type with a motor of 10 HP. The main results obtained from the experiments are summarized as follows. 1) Some experimental results on the wave overtopping on a vertical seawall in condi- tions of calm are described for the wave steepnesses of 0.01, 0.02 and 0.03, and compared with those by Ishihara, Iwagaki and Mitsui, and Saville. 2) When incident waves do not break in front of the seawall, the quantity of wave overtopping begins to increase suddenly with an increase in the wind velocity at a certain wind velocity. The increasing segment of quantity of wave overtopping by wind is considerable compared with other cases. 3) When incident waves break just in front of the seawall, the quantity of wave overtopping changes complicatedly with an increase in the wind velocity for the wave steepness of 0.01, and it becomes approximately constant over a low wind velocity for the wave steepness of 0.02. 4) When incident waves break before they rearch the seawall, the effect of wind on wave overtopping is not very great. and in particular when the seawall is constructed at the shoreline or on shore, the quantity of wave overtopping tends to decrease a little at a high wind velocity. 1. Introduction In determining the design height of a seawall or seadike, the allowable quan- tity of wave overtopping on it should be estimated, based on the conditions of its hinterland, the structural type of the seawall and the drainage facilities". Up to the present, the design height of a seawall or seadike has been decided by a simple method whereby the height is the sum of the design high water level, the height of wave run-up calculated from the design wave height, and an extra height for safety',"'. The method for determining the design height of a seawall or seadike based on the quantity of wave overtopping has not 12 Y. IWAGAKI. Y. TSUCHIY A and M. INOUE been established yet. This is considered to be caused by very complicated phenomena of wave overtopping associated with many hydraulic factors, and the mechanism of wave overtopping has not been completely investigated. With regard to the studies of wave overtopping on seawalls or seadikes, Saville and Caldwell"' first carried out some experiments on wave overtopping on vertical seadikes in 1953, and consequently in 1955, many experiments for seawalls with various shapes were carried out by Saville. In the same year, Sibul°' tried a few experiments in the same manner for inclined seadikes. In 1956, Sibul and Tickner" carried out model experiments for seadikes with slopes of 1/3 and 1/6 put on a model beach with a slope of 1/10 to find the additional quantity of wave overtopping due to the action of wind, compared with conditions in calm weather. He concluded from the result of the experi- ments that the smaller the inclination angle of a seadike, the greater was the influence of wind on wave overtopping. Paapes' made clear, by using a wind wave tunnel, that the irregularity of incident wind waves increases the quantity of wave overtopping considerably, compared with the results in the case of regular waves. However, the influence of wind on wave overtopping has not yet been made clear quantitatively. In Japan, Ishihara, Iwagaki and Suzuki" asserted in 1955 that a design method considering the allowable quantity of wave overtopping to some extent, should be used for practical purposes, and Ishihara, Iwagaki and Mitsui91 measured systematically the quantity of wave overtopping on vertical and inclined seadikes when there was no wind. They proposed a new dimensionless expression for the quantity of wave overtopping, which is different from the expression pro- posed by Saville. The details of the analysis of experimental results will be explained in Chapter 3. Recently, Iwagaki and others"),'" discussed the effects of wave characteristics, water depth and water level on the quantity of wave overtopping on vertical seawalls, based on their experimental results, in addition to those by the Beach Erosion Board. As mentioned above, most of the studies on wave overtopping on seawalls and seadikes are experimental as in U. S. A. and Japan, but in particular ex- periments in calm weather have produced considerable results. However, the phenomenon of wave overtopping associated with strong wind during storm has not been studied sufficiently. For this reason, the authors have begun a basic study of wave overtopping by the high-speed wind-wave tunnel, newly constructed in 1961 at the Ujigawa Hydraulic Laboratory, to disclose the influence of wind on the quantity of wave overtopping. This paper is the first report of the study in which the experi- mental equipments used are described, and some results of the experiments for vertical seawalls in the case of the wave steepnesses of 0.01 and 0.02 arc presented. 2. Experimental Equipments (1) High-speed wind-wave tunnel In 1961, the high-speed wind-wave tunnel was constructed to study the fol- lowing three matters : firstly the hydraulic performance of seadikes and sea- On the Effect of Wind on Wave Overtopping on Vertical Seawalls 13 walls against waves during storm, secondly the generation and growth of wind waves, showing especially how the shearing stress with which high speed wind acts on a water surface, changes with increase of wind speed, and thirdly to study the wind resistance of structures. In this section, the wind wave tunnel, the blower and the wave generator are explained in outline. (a) Wind wave tunnel This wind wave tunnel is divided into three parts ; the first is a so-called wind wave tank to study hydrodynamical characters of wind waves and mechanism of wave overtopping on seadikes, the second the smoke tunnel to study the wind resistance of structures and the third the wind tunnel to generate wind. A distinctive character of the high-speed wind-wave tunnel is that both the wind wave tank and the smoke tunnel can be operated by a blower. The wind wave tunnel consists of a wind blower, a wind tunnel, a wind wave tunnel and a smoke tunnel. The wind blower consists of an electric motor, a fan, moving vanes, fixed vanes, and an inner cylinder. The wind tunnel consists of a divergence tunnel, a baffle screen, a branch tunnel, and a nozzle. The smoke tunnel consists of a main tunnel, a baffle screen, an observation tunnel, and a nozzle. The downstream end of the wind tunnel is connected with a wave tank 40 m long, 2.3 m to 4.0 m high and 0.8 m wide. A part of the wave tank 0.3 in deep is submerged in the ground. Experiments on the wave overtopping are carried out at about 1.0 m in water depth. In this case, a model structure is put on a model sloping beach with a slope of 1/15 j i 1 11 I 1 i - ___Now „'ElmN,NININm•s•EppENIENmesomUremMtNINOII Sal OAEs,IMMin „Tim/a-1—.1---.._. /^ ^ ^ .....„-.1.,_...,03i104,iiiila „A..,...,.,..,, _ ,-I) II II II II t:'___i 1 I ^^ia. sim1111^11111MinillM _.i Planavq.arentsWirdImpel irli O. 1 Smokelam& N.- I I r c"ter Fig. 1 Sketch of high-speed wind-wave tunnel. I t : t f-"lilt-S sl :I '°11''art% -S*,,,"-,At Cr', I %' . ,; c ' ,, :„.*"11 , 41,-,,e,,,,,'xv-1, .., ,7 ` -T- .1° a; "I'' Photo. 1 General view of high-speed wind-wave tunnel. !' 14 Y. IWAGAKI,Y. TSUCIIIYA and M. INOUE at the end of the wave tank, so the height of ceiling made of aluminum was gradually varied. A wave generator is set near the wave tank and connected with it, so that waves can be generated without operating the blower. Fig. 1 shows a sketch of the wind wave tunnel and Photo. 1 indicates a general view of the wind wave tank. (b) Electric motor and blower The motor is a varying speed commutator motor of three-phase current shunt type, 100HP,and the rotating speed can be adjusted continuously from 350r.p.m. to 1,000r.p.m.
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